Can I really use old cooking oil?!

Yes – but a strong word of caution. Used vegetable oil (UVO) will contain impurities such as water, acids, particles of food plus dissolved animal fats. The acids will attack the metal surfaces of a fuel injection system, whilst animal fat content will cause used oil to solidify at cooler temperatures. Impurities, acids and high water content will lead to rapid aging and even failure of your expensive injection system.

If your vehicle is of the older, non-common rail type you might consider the risks associated with UCO acceptable. Regenatec strongly recommends against the use of home prepared UCO in a common rail / direct injection engine. Should you consider the use of UCO an acceptable risk, the following should be bourn in mind:

Regulating acidity levels in used oil is hardest thing to get right in a home set up. Commercially, this is done by using a bentonite filter element, commonly known as 'Fullers Earth' in the UK. You can find out more at Wikipedia (http://en.wikipedia.org/wiki/Bentonite#Calcium_bentonite).

UCO can produce the same performance as fresh oils but due to the highly variable nature of the quality, highly variable results can be expected.

Another reason against the use of UCO is that of vehicle fuel starvation caused by what’s termed fuel filter ‘plugging’. This is where the flow of fuel through the filter has be reduced to a rate below that which the engine demands, due to the presence of solid contaminants or build of wax like components from the UCO. Filter plugging is noticeable at times of maximum fuel demand: high speed cruising, high acceleration or carrying a heavy load.

There are two ways to avoid filter plugging with UCOs:

1. Cold filter the UCO through a filter of smaller dimensions than the one used on the vehicle. In practice most vehicle fuel filters are of the 5 – 15 micron particulate size, although there’s a move toward filters as fine as 1 micron on some newer common rail engines (as injector nozzle bore sizes become smaller to achieve finer droplet sizes in cylinder). We therefore strongly recommend that your final filter stage be a cold filter of 1 micron. (See the Accessories section in the smartveg shop for suitable filters).

2. Use a heated fuel filter on the vehicle. There’s a strong temptation to warm filter UCO to reduce filter times and increase yield. However, this essential dissolves the fatty waxes that only reform when the oil cools – and then exist to plug the vehicle’s fuel filter when introduced to the vehicle. By using a heated fuel filter that’s warmed to a temperature greater than that of the filter rig will ensure these temperature dependant waxes do not form in the fuel filter. (See the Accessories section in the smartveg shop for a suitable coolant-fed heated fuel filter).

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